Various instabilities and chaotic mixing in channel flows

dr Stanisław Gepner

Warsaw University of Technology, MEiL

Nov. 15, 2019, 1:15 p.m., ul. Pasteura 5, B0.14

Improvements in the performance of various flow-based devices, such oxygenators or DNA microarrays can be reduced to decreasing hydraulic drag and increasing achievable mixing efficiency. In case of fluids, mixing can be seen as an inter-material transport process (such as diffusion) overlaid on top of “mechanical” stirring that results from kinematics of the flow. Since, in general diffusion is relatively slow, the role of stirring is to cause generation of small-scale structures that can be quickly smoothed out by diffusion. This can be efficiently achieved via turbulization. Still, there are a few problems for which this is unfeasible, either due to size constraints or fragile nature of processed materials. In case of laminar flows effective stirring can be achieved by principles of chaotic advection. Chaotic advection is a phenomenon in which fully laminar, relatively simple velocity fields (in the Eulerian representation) result in chaotic response in the Lagrangian view. High complexity of motion, in case of such flows, results from the fact that dynamical system that describes motion of individual fluid particles might be non-integrable leading to the onset of chaotic trajectories and in consequence improved stirring. The objective of this work is to study the onset of chaotic advection due to amplification of naturally occurring hydrodynamic instabilities resulting from large-scale wall corrugations. At the same time, we plan to examine and quantify possible improvements of mixing due to chaotic character of advection.